Every 3-Manifold with Boundary Embeds in Triod × Triod × I
Li Zhongmou · Proceedings of the American Mathematical Society · 1994
Li Zhongmou, Every 3-Manifold with Boundary Embeds in $\operatorname{Triod} \times \operatorname{Triod} \times I$, Proceedings of the American Mathematical Society, Vol. 122, No. 2 (Oct., 1994), pp. 575-579